This invention relates to ink-jet printing and, more particularly, to a technique for achieving accurate color printing while balancing use rates of individual colorants.
Color ink-jet printers typically make use of four or more inks to reproduce a specified color. Colors to be printed are often specified in terms of a red, green, and blue (RGB) color description typically used by a computer for displaying color images on a monitor. The inkjet printer, in contrast, forms images which are specified typically in terms of colorants such as cyan, magenta, yellow, and black inks (CMYK). Therefore, the color specification in terms of RGB tone values must be converted into cyan, yellow, magenta, and black ink droplets that when properly deposited on media faithfully reproduces the RGB specified color.
Techniques exist for conversion of the RGB signals into corresponding CMYK inks as well as signals for controlling the printer to eject these inks in the proper manner. The printing system typically makes use of a printhead or drop ejector portion that is frequently mounted within a carriage that is moved back and forth across a print media, such as paper. As the printhead is moved across the print media, a control system activates the printhead to deposit or eject ink droplets onto the print media to form images and text.
The printhead is sometimes mounted to an ink container that supplies ink to the printhead. This ink container is sometimes a multi-chamber ink container that contains more than one ink. These multi-chamber ink containers typically contain one or more of the following inks: black, cyan, yellow, and magenta. Each chamber of the multi-chamber ink container is then fluidically coupled to the drop ejection device or printhead.
One shortcoming of the multi-chamber ink container is that when any of the ink chambers of the multi-chamber ink container is depleted of ink, the entire ink container must be replaced. The ink container must be replaced because the printing system is no longer capable of faithfully reproducing the RGB color descriptions. Discarding the entire multi-chamber ink container prevents the remaining inks in the other chambers from being used, creating waste. This waste is exacerbated if the use rate on any one ink is abnormally high, thereby causing that particular ink to be exhausted well before the other inks. Replacing the entire multi-chamber ink container not only results in discarding unused ink, but in the case where a printhead is mounted to the multi-chamber ink container, discarding the multi-chamber ink container also results in discarding the printhead in which at least portions thereof have not reached end-of-life.
One solution has been to use a black ink chamber that is of greater volume than a volume associated with the other inks. Printers used in typical business applications tend to print more text than graphics, thereby requiring larger volumes of black ink. Where the black ink container is included in a multi-chamber arrangement, this solution reduces waste for those users that require large volumes of black ink. However, for those users who consume black and color inks more evenly, such as in the case of graphics printing, this solution exacerbates the waste problem. For the case where the black and color inks are used more evenly, a greater volume of black ink is unused resulting in the waste of a large amount of black ink.
There is an ever-present need for ink-jet printing systems that have relatively low manufacturing costs that are also economical to operate. These printing systems should be well suited for a wide variety of printing applications such as text and graphics printing. Finally, these printing systems should not require frequent intervention by the consumer such as to replace empty ink containers and should be capable of minimizing ink waste.